The invention disclosed herein relates generally to verifying communications paths on a network. More particularly, the present invention relates to forwarding a test signal between network nodes to evaluate quality of service in an Internet Protocol (“IP”) telephony system.
The Open Systems Interconnection (OSI) specification provides a “reference model” for how messages should be transmitted between any two points in a telecommunication network. The purpose of the model is to guide product technology implementers so that their products will consistently work with other products. The reference model defines seven layers of functionality that take place at each end of a communications link. Layer 3 (“L3”) refers to the network layer of the model, which is concerned with knowing the address of neighboring nodes in a network, selecting routes and quality of service (“QoS”), and recognizing and forwarding to the transport layer incoming messages destined for the local host. An Internet Protocol address is one example of a layer 3 address.
In Internet telephony systems, such as voice over IP (“VoIP”) networks, quality of service between network nodes is an important concern. If the quality of service is too low, for example due to latency or the unavailability of a network node, then users may not be able to place calls or their calls may be distorted. Tools such as Ping (Packet Internet or Inter-Network Groper) are used to verify that a given IP address exists and can accept requests. Users and software processes employ Ping to diagnostically ensure that a host computer that the user is attempting to reach is actually operating. Ping may also be used to communicate with an operating host in order to determine the amount of time required to receive a response from the host, as well as other related statistics. The Ping software utility sends an Internet Control Message Protocol (ICMP) packet to a specified IP network address or a qualified domain name. ICMP is an extension to the IP protocol that supports packets with error, control and informational messages. The utility waits for replies from the address in response to receipt of the ICMP packet.
Current tools such as Ping, however, do not provide information regarding the state of connections between nodes based on information derived from an actual call placed on the network. Instead, these tools provide quality of service data inferred from the statistics gathered which may not be as accurate as data derived from an actual call.
Other tools such as those described in the above-referenced application Ser. No. 09/855,156 and application Ser. No. 09/826,697 do provide quality of service data inferred from data derived from an actual call. These tools, however, use reference files and other methods to test the quality of service at a particular network device, but they do not test the quality of service between network devices on a network path or in a loop of network devices. There is thus a need for a system and method that provides quality of service information for a VoIP network based on actual call data in a loop of network devices.